Enhancing apple disease resistance via magnetic nanoparticle-mediated delivery of artificial miRNAs that suppress a tRNA-derived small RNA targeting a disease-resistant gene

Apple early defoliation disease poses a serious threat to the sustainability of global apple production, causing substantial yield losses and reduced fruit quality. Chemical fungicides remain the primary means of disease control; however, their excessive use leads to environmental pollution and food safety concerns. Here, we identified a pathogen-induced tRNA-derived small RNA (tsRVal) that targets the disease-resistance gene Malus domestica TRANSPORT INHIBITOR RESPONSE 1 (MdTIR-1), thereby modulating apple susceptibility to early defoliation disease. To suppress tsRVal accumulation, we designed an artificial miRNA (si-tsRVal) and loaded it onto Fe₃O₄ magnetic nanoparticles (MNPs) to form stable spherical complexes (MNP-si-tsRVal). The MNP system efficiently delivered si-tsRVal plasmids into apple leaf cells via foliar spraying, as confirmed by transmission electron microscopy analyses and energy-dispersive spectroscopy. In both potted seedlings and field-grown trees, plants treated with MNP-EV exhibited severe leaf drop, whereas MNP-si-tsRVal-treated plants retained healthy foliage and vigor. Collectively, these results demonstrate that MNP-si-tsRVal enhances resistance to early defoliation disease, providing durable protection and a sustainable alternative to chemical fungicide application.